It's particularly bad when they stop telling you what clock speeds are achievable with more than one core active. At best these days you get a "base clock" spec that's very slow that doesn't correspond to any operating mode that occurs in real life. You used to get a table of x GHz for y active cores, but then the core counts got too large and the limits got fuzzier.

And laptops have another layer of bullshit, because the theoretical boost clocks the chip is capable of will in practice be limited by the power delivery and cooling provided by that specific machine, and the OEMs never tell you what those limits are. So they'll happily take an extra $200 for another 100MHz that you'll never see for more than a few milliseconds while a different model with a slower-on-paper CPU with better cooling can easily be more than 20% faster.